Method of manufacturing an electric discharge tube and discharge tube obtained in this manner

ABSTRACT

In manufacturing an electric discharge tube recesses are provided in the wall of the tube by means of sandblasting or liquid honing. The electrodes of the electrode system of the tube are fixed in said recesses the shape and orientation of which are determined by a mask.

United States Patent [19] van Esdonk et al.

[ Dec. 23, 1975 METHOD OF MANUFACTURING AN ELECTRIC DISCHARGE TUBE AND DISCHARGE TUBE OBTAINED IN THIS MANNER Inventors: Johannes van Esdonk; Johannes Assignee:

Filed:

Appl. No.

Petr-us Homman; Franciscus Cupertinus Maria de Hass, all of Eindhoven, Netherlands U.S. Philips Corporation, New York, NY.

Aug. 14, 1973 Foreign Application Priority Data Sept. 27, 1972 Netherlands 7213022 US. Cl. 313/249; 29/2516; 51/283;

51/318; 313/244; 313/252 Int. Cl. H01J 1/88; HOlJ 19/42 Field of Search 313/249, 78, 81, 244, 245, 313/252, 253; 315/3975; 51/317, 318, 319, 51/283;29/25.16,25.15

Primary ExaminerSaxfield Chatmon, Jr. Attorney, Agent, or FirmFrank R. Trifari; George B. Berka [57] ABSTRACT In manufacturing an electric discharge tube recesses are provided in the Wall of the tube by means of sandblasting or liquid honing. The electrodes of the electrode system of the tube are fixed in said recesses the shape and orientatio'rifof which are determined by a mask.

3 Claims, 6 Drawing Figures e. \F L US. Patent Dec. 23, 1975 Sheet 1 of2 3,928,782

Fig.1

V I 31 32 33 30 Y[ Fig.3

US. Patent Dec. 23, 1975 Sheet 2 of2 3,928,782

METHOD OF MANUFACTURING AN ELECTRIC DISCHARGE TUBE AND DISCHARGE TUBE OBTAINED IN THIS MANNER The invention relates to a method of manufacturing an electric discharge tube in which one or more recesses are provided in the wall of the tube and by means of which at least one component of the electrode system of the tube is fixed with respect to other components.

The invention furthermore relates to an electric discharge tube obtained by the above method.

The fixing of electrodes by means of grooves provided in the wall of the tube is known from the German Patent Specification No. 872,610. One of the advantages of such a method is that an electrode system can be constructed in a rapid and simple manner. In assembling an electrode system, only very small tolerances in the mutual distances of the electrodes may be permitted. This means that high requirements are imposed upon the accuracy with which the grooves are provided in the wall of the tube and in particular upon the accuracy with which the grooves are provided at a mutual distance from each other or with respect to a certain reference in the tube. However, methods which might be considered for providing such grooves are not stated in the said patent specification.

A similar method of fixing electrodes in a cathoderay tube is known from the U.S. Pat. Specification No. 3,047,759. In this method, the grooves for fixing the electrodes are obtained by grinding or moulding on the concave side of each of two semi-tubular parts fitting on each other. These methods exhibits drawbacks. For example, when the material to be machined is glass, stresses are introduced into the glass by the forces exerted during grinding, which stresses may afterwards result in cracking. A drawback of moulding or pressing is that it must be possible for the workpiece to be easily detached from the mould used. This presents great problems if the grooves have to be provided on the inside of a hollow tube. This presents problems in particular with tubes having a small inner diameter.

Another known method, for example, etching, is suitable indeed for accurately providing grooves, but it suffers from the drawback that the operation is particularly time-consuming and therefore very expensive.

It is the object of the invention to provide a method in which recesses can be provided in an accurate and simple manner in glass, ceramics, metal or another hard material without the said drawbacks occurring.

For that purpose a method of the type mentioned in the preamble is characterized according to the invention in that the recesses are provided in the wall of the tube by exposing it to the action of particles of grinding material incorporated in a flow of gas or liquid.

Such a method is generally referred to as sand-blasting when the grinding material is incorporated in a gas flow, and as liquid honing when the grinding material is incorporated in a flow of liquid. These denominations will also be used hereinafter on the understanding that the particles of grinding material are not restricted to sand grains but in principle may consist of any suitable granular material, for example, aluminium oxide powder. Sand-blasting and liquid honing presents a few advantages over the already mentioned methods. The said recesses are obtained in a particularly rapid and in particular in a simple manner. These recesses do not show any sharp edges or abrupt transitions. This is particularly favourable-since in the case of glass tubes an abrupt transition easily results in fracture, while sharp edges during fixing the electrodes easily crumble away so that loose particles may land in the tube. The use of these methods presents no problem whatsoever in providing recesses on the inside of hollow tubes having small inner diameters.

It is to be noted that sand-blasting and liquid honing are known methods which are used in particular in surface treatments, such as frosting and cleaning, of hard materials. However, in these comparatively rough treatments accuracy hardly plays a part. Possibly because sand-blasting is generally considered as a rather coarse treatment, said method has never been used in the manufacture of articles which are subject to particularly small tolerances. As regards the liquid honing it is to be noted that it is known from Dutch Patent application No. 6709115 to provide a groove in the wall of a television display tube by means of this method, which groove extends coaxially with the axis of the tube. However, in this case it deals with an accurately defined local weakening in the wall of the display tube. However, accuracy with respect to the place of the groove is out of order.

In the method according to the invention a mask is preferably used. With said mask, the shape and orientation of the recesses are accurately determined since therewith the surfaces adjoining said recesses are protected from the action of the particles of grinding material. Such a mask may be formed, for example, by one or more hollow cylinders which are slid so as to fit closely in the tube to be provided with grooves and which are fixed in the tube with respect to a certain reference. The hollow cylinders themselves show slots or holes which have a shape corresponding to that of the desired recesses. Furthermore, the said hollow cylinders are manufactured from material which is resistant to detrition, such as nylon or linen soaked in resin.

It is to be noted that the use of masks is known in manufacturing ornaments on glass articles by means of sandblasting. Not counting the fact that in this case we have to do with a totally different field of activity, it moreover deals with comparatively superficial treatments in which no great accuracy is required.

According to the invention, the recesses in the wall of the tube are preferably sand-blasted. This is done because liquid honing in the first place is a less clean operation and in the second place because the liquid with the particles of grinding agents suspended therein easily penetrate between the mask and the wall of the tube. As a result of this, scratches could be formed in the wall of the tube upon removing the mask, which scratches in the case of a glass tube could even result in fracture as a result of temperature fluctuations.

According to the invention, the recesses in the wall of the tube are preferably sand-blasted by means of powdered aluminium oxide. Good results have been obtained with grinding material having an average grain dimension between 10 ,um and 20 ,um, and a largest grain size of at most 30 pm. A sufficiently smooth bottom of the recesses without abrupt transitions is obtained with such a grain size, while tolerances of 50 um in the mutual distance of the recesses can be fulfilled as such.

The invention will be described in greater detail with reference to a drawing, in which FIG. 1 is an axial sectional view of a part of an electric discharge tube during the performance of a method according to the invention;

FIG. 2 shows on an enlarged scale a sectional view of the coaxial groove 9 in FIG. 1;

FIG. 3 is an axial sectional view of a part of an electrode system mounted in a discharge tube manufactured according to the invention;

FIG. 4 is a sectional view taken on the line IV-IV,

FIG. 5 is a sectional view taken on the line V-V, and

FIG. 6 is a sectional view taken on the line VIVI of the discharge tube of FIG. 2.

In FIG. 1, a glass tube 1 having a wall thickness of 1 mm and an inner diameter of 14 mm is clamped on a device which is not shown in the drawing. By means of this device the tube 1 can be moved axially according to the double arrow 2 and rotated about its axis in the direction of the arrow 3. Particles of aluminium oxide incorporated in a flow of air are blown to a nozzle head 6 having a nozzle 7 via a nylon hose 5 at a pressure of '6 atm. in the direction of the arrow 4. By means of the nozzle 7 which has an inner diameter of 0.4 mm, the aluminium oxide grains 8 which have an average grain dimension of 17 um are directed on the glass wall of the tube 1. By simultaneously rotating the tube 1 about its longitudinal axis, a groove 9 having a width of 0.5 mm and a depth of 0.4 mm is obtained coaxially with the tube axis. By means of a mask formed by the hollow cylinders 10 and 11 consisting of a resin and having a wall thickness of 0.8 mm, the place and width of the groove 9 are accurately determined. The grooves 12 which extend in the axial direction have been obtained by moving the tube 1 in the axial direction during the sand-blasting operation. The shape and the place of the grooves 12 are accurately determined by the slots 13 present in the hollow cylinder 11. After the desired recesses have thus been provided, the hollow cylinders 10 and 11 are removed from the tube 1. The glass tube 1 is then rinsed in a hexane bath by means of ultrasonic vibrations and the various electrodes are finally fixed in the grooves 9 and 12. A characteristic feature of recesses obtained by sand-blasting or liquid honing is that they do not show sharp edges or abrupt transitions. The groove 9 of FIG. 1 which is shown in an enlarged crosssectional view in FIG. 2 shows rounded corners at 14 and 15. These facilitate not only the fixing of the electrodes but the removal thereof is also considerably simplified. The latter operation is necessary when an electrode has to be moved over one or more recesses before it reaches its place of destination.

It is to be noted, in particular with respect to said movement of an electrode, that the formation of separate particles in the tube is avoided by the rounded corners of a recess.

FIG. 3 is an axial sectional view of a part of an electric discharge tube manufactured according to the invention. In the manner described above, a few recesses are provided on the inside of the hollow glass tube 20, in which recesses the electrodes 21, 22 and 23 are fixed. Four resilient lugs 24 are spot-welded at one end to the electrode 21 to be fixed. The other end of each lug 24 bears in a recess 25 provided in the wall 20. Since the lugs 24 are slightly resilient in the radial direction, the electrode 21 can be inserted at one open end of a tube 20. In the place of destination, the lugs 24 snap into engagement with the recesses 25 destined for this purpose. The cross-sectional view of FIG. 4 shows this once again.

If locking against rotation of an electrode is not necessary, a groove extending coaxially with the axis of the tube may ensure the fixing of the electrode as is the case for electrode 22. Like electrode 21, electrode 22 shows a number of resilient lugs 26 which snap into engagement in the coaxial groove 27 as is shown in FIG. 5.

Still another possibility of fixing an electrode is used in a gauze electrode 23. Such an electrode often forms part of the electrode system of a television camera tube of the vidicon type. A gauze 23 clamped between two rings 28 during a thermal treatment is held in its place in that the rings 28 themselves are clamped between two locking springs 29 which each snap into engage ment with a coaxial groove 30. Such a way of fixing which is shown again in the cross-sectional view of FIG. 6, ensures a perpendicular position of the gauze electrode 23 relative to the axis of the tube.

A number of electrodes 31 provided on the wall of the tube by vapour deposition or chemically can particularly readily be combined with the other electrodes. The holes for the electric lead-throughs 32 have been obtained in the same operation and by means of the same mask as the above-described recesses. In this case the axial groove 33 does not serve as a fixing possibility for an electrode but is provided with a view to increasing the leakage path between the electrodes 31 so that higher electric potentials for the electrodes 31 can be permitted.

What is claimed is:

1. A method of manufacturing an electric discharge tube having a plurality of recesses in its inner wall for holding supporting parts of the electrode system of the tube, comprising the steps of: fixing into the tube relative to a reference point a mask having openings corresponding to the shape and mutual displacement of the recesses to be created, and exposing the uncovered wall portions of the tube to the action of a jet of particles of grinding material incorporated in a fluid until the recesses are created.

2. A method as claimed in claim 1, wherein said jet includes particles of aluminum oxide incorporated in a gas flow.

3. A method as claimed in claim 2, wherein the particles of aluminium oxide have a grain size between 10 tmand30um. 

1. A method of manufacturing an electric discharge tube having a plurality of recesses in its inner wall for holding supporting parts of the electrode system of the tube, comprising the steps of: fixing into the tube relative to a reference point a mask having openings corresponding to the shape and mutual displacement of the recesses to be created, and exposing the uncovered wall portions of the tube to the action of a jet of particles of grinding material incorporated in a fluid until the recesses are created.
 2. A method as claimed in claim 1, wherein said jet includes particles of aluminum oxide incorporated in a gas flow.
 3. A method as claimed in claim 2, wherein the particles of aluminium oxide have a grain size between 10 Mu m and 30 Mu m. 